/ Field knowledge · IMC 501.4
Exhaust without a makeup path is a pressure problem.
IMC 501.4: size exhaust for the required airflow and run it whenever exhaust is required. For spaces other than Group R-3 and dwelling units in Group R-2, keep the space neutral or negative. Door undercuts are not a makeup-air strategy for large offsets.
Educational 2024 IMC 501.4–501.5. Confirm adopted edition. This is not a pressurization design. Kitchen Type I replacement air is still IMC 508. Packet: 501.4 PDF · ES.
- If supply > exhaust, provide a relief path (natural or mechanical) for the excess.
- If exhaust ≥ supply (or exhaust-only), provide makeup air to cover the deficit — OA, transfer, or dedicated MAU, drawn.
- 501.5: when this section doesn’t specify construction, follow Chapter 6 for duct materials, gauges, joints, supports, fire/smoke, terminations.
Exhaust-only rooms
Bathrooms, janitor closets, telecom: confirm a documented makeup path (undercut, transfer grille, or mechanical OA). If exhaust exceeds supply, the space goes negative and contaminant migration follows. Show pressure intent on M-101 (N / NEG / BAL).
Source: DCT 501 Part 4 · tool: pressure / makeup check · undercuts: 601.5 jump ducts · kitchen: 508.
What to send
Room list with exhaust and supply if known, whether doors are undercut, and whether a hood is in play.
If doors whistle or the hood will not capture
Send the exhaust/supply split and the floor plan. MasterBuild will say whether this is 501.4, 508, or a transfer path that was never drawn.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
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